I'd second other commenters in that you should get your sleep checked out. I had unchecked sleep apnea for about a year and wasn't able to learn or remember anything during that period. Sleep apnea is very subtle, some people go untreated for decades and are shocked to find they have it. I was 26 when I was diagnosed, lean, and otherwise in great shape—so, really, anyone could fall victim—it's worth looking into. Further reading: https://www.menshealth.com/health/a19532060/sleep-apnea-coul...